Image decoding method, image coding method, image decoding apparatus, and image coding apparatus

Abstract

An image decoding method for decoding an image including slices while reducing both a decrease in image quality and a decrease in coding efficiency is provided. The image decoding method includes: decoding a current motion vector which is a motion vector of a current block to be decoded and specifies a reference block included in a reference picture, and a difference image block indicating a difference between the current block and a prediction image block; generating the prediction image block by allocating, to an outside pixel that is a pixel included in the reference block and located outside an associated slice that is a slice corresponding to a current slice to be decoded which includes the current block, a value of an inside pixel that is a pixel located inside the associated slice; and adding up the difference image block and the prediction image block to reconstruct the current block.

The invention claimed is: 
     
       1. An image decoding method for decoding, on a per-block basis, pictures each including slices, the method comprising:
 decoding a current motion vector and a difference image block, the current motion vector being a motion vector of a current block to be decoded and specifying a reference block included in a reference picture, and the difference image block indicating a difference between the current block and a prediction image block; 
 generating the prediction image block by allocating a value of an inside pixel to an outside pixel, the inside pixel being a pixel located inside an associated slice, the outside pixel being a pixel located outside the associated slice and included in the reference block specified by the current motion vector, and the associated slice being a slice included in the reference picture and corresponding to a current slice to be decoded which includes the current block; and 
 adding up the difference image block and the prediction image block to reconstruct the current block. 
 
     
     
       2. The image decoding method according to  claim 1 , comprising
 storing, into a memory unit, identification information for identifying a range of the associated slice specified in each of reference pictures, 
 wherein in the generating, the outside pixel and the inside pixel are determined by referring to the identification information stored in the memory unit, and the value of the inside pixel is allocated to the outside pixel to generate the prediction image block. 
 
     
     
       3. The image decoding method according to  claim 2 ,
 wherein in the decoding, the identification information is decoded, and 
 in the storing, the identification information resulting from the decoding is stored into the memory unit. 
 
     
     
       4. The image decoding method according to  claim 2 ,
 wherein in the storing, the identification information is stored into the memory unit when the range of the associated slice has been changed. 
 
     
     
       5. The image decoding method according to  claim 1 ,
 wherein in the decoding, applicability information is decoded, the applicability information indicating whether or not the value of the inside pixel is to be allocated to the outside pixel of the reference block, and 
 in the generating, when the applicability information indicates that the value of the inside pixel is to be allocated to the outside pixel, the value of the inside pixel is allocated to the outside pixel of the reference block to generate the prediction image block. 
 
     
     
       6. The image decoding method according to  claim 5 ,
 wherein the decoding includes decoding the applicability information indicating whether or not the value of the inside pixel is to be allocated to the outside pixel of the reference block which includes a boundary of the associated slice, and 
 in the generating, when the applicability information indicates that the value of the inside pixel is to be allocated, the value of the inside pixel is allocated to the outside pixel of the reference block which includes the boundary of the associated slice, to generate the prediction image block. 
 
     
     
       7. The image decoding method according to  claim 5 ,
 wherein the decoding includes decoding the applicability information indicating whether or not the value of the inside pixel is to be allocated to the outside pixel of the reference block which is entirely included in a non-associated slice different from the associated slice, and 
 in the generating, when the applicability information indicates that the value of the inside pixel is to be allocated, the value of the inside pixel is allocated to the outside pixel of the reference block which is entirely included in the non-associated slice, to generate the prediction image block. 
 
     
     
       8. The image decoding method according to  claim 1 ,
 wherein in the decoding, an offset value for shifting the associated slice is decoded, and 
 in the generating, the associated slice is shifted by as much as the offset value, and the value of the inside pixel which is a pixel located inside the associated slice resulting from the shifting is allocated to the outside pixel which is a pixel located outside the associated slice resulting from the shifting, to generate the prediction image block. 
 
     
     
       9. The image decoding method according to  claim 1 ,
 wherein in the generating, the value of the inside pixel which is a pixel spatially closest to the outside pixel among pixels included in the associated slice is allocated to the outside pixel, to generate the prediction image block. 
 
     
     
       10. An image coding apparatus comprising a processor which performs the image decoding method according to  claim 1 .